Wood is exposed to various biotic and abiotic factors of decay. These processes are necessary and required in the nature, but when wood is used for construction purposes, we would like to slow them down as much as possible. This is can be achieved by using chemical wood preservatives.
Most of the Slovenian and European wood species produces wood that is not resistant against fungi, insects and termites. If we want to use such wood in hazard class 3 (wood above soil, uncovered) or hazard class 4 (soil or water contact), we have to chemically protect it. Proper treatment prolongs lifespan of wood, what results in cheaper maintenance and safety of wooden construction.
Copper effectiveness against wood decay fungi makes it important constituent of wood preservatives for almost 200 years. In recent years, the use of copper compounds for biocidal purposes has increased. The reasons are: copper compounds are relatively safe, development of pathogens has been minimal; pathogens show increased tolerance against organic fungicides after extended period of use, and thirdly increase in government regulations and restrictions (or outright banning) of alternative products due to their toxicological or environmental impacts. However, traditional copper based wood preservatives had an important drawback; copper did not get fixed into wood and was prone to leaching out of wood.
This problem was resolved, by introducing of fixed water-borne preservatives. Heinrich Bruning discovered that normally soluble metal salts could be made insoluble, or fixed inside wood, by addition of large amounts of chromium. Since carcinogenic nature of chromium compounds is well known, most of the European countries intend to ban use of chromium in wood preservatives. Some of them will allow use of chromium preserved wood only for special purposes that are classified as hazard class IV. Use of chromium based wood preservatives will be banned for children playground equipment, garden furniture. Therefore, intense researches are going on in the world laboratories to develop environmentally acceptable solution for copper fixation in wood preservatives.
Ammonia was found very effective copper fixative long time ago, but due to its emissions this formulation newer came into extensive commercial use. Later ammonia was replaced with amines; particularly ethanolamine and triethanolamine were found very effective copper fixative. Commercial wood preservatives on the basis of copper and ethanolamine are available on the market already. However, copper leaching from such treated wood is still 5-10 times higher than leaching from wood treated with classical copper-chromium based preservatives.
Beside problems with copper fixation, use of copper treated wood is limited because of appearance of copper tolerant fungi as well. Therefore co-biocides are introduced to copper-ethanolamine based aqueous solution to increase protection against copper tolerant fungi. Addition of co-biocides is very tricky, as we have to pay attention not to increase copper leaching.
There are several copper based wood preservatives available on the market. In the major part of the countries (Russia, Ukraine, Africa, Asia, and South America) still uses wood preservatives based on copper, chromium and arsenic salts. American wood preservative association introduces abbreviation CCA for such preservatives. In most of these aqueous solutions copper is in the form of copper oxide. Copper in those preservatives served as fungicides, arsenic as insecticide and secondary fungicide and chromium as fixative. These types of preservatives are available under different commercial names such as: (Celcure A, Tanalith C, Ascu-Greensalts, Wolman CCA, OsmoseK33, Langwood.
In the continental part of Europe, arsenic salts are banned for almost 15 years. In order to ensure protection of wood against insects, boron salts were introduced instead. In some of the Scandinavian countries arsenic was replaced by fluorine compounds.
In the USA besides copper-chromium based preservatives other solutions are used as well. One of them consists of copper, arsenic and ammonium acetate. After 1983 part of arsenic was replaced with zinc. Fixation of these preservatives is very simple; most of copper participates after volatilization of ammonia.
In the eighties, there were preservatives consisting of copper, arsenic and ammonia. Due to unpleasant ammonia emissions, workers on the impregnation systems do not want to use it.
However, completely new solution was developed in Wolman. They developed solution consisting of Cu—HDO (copper hydroxyquinolinolate), that is soluble in solutions with pH value above 7, but precipitates in insoluble form if pH decreases below 6. In acidic wood, copper precipitation appears, rapidly after impregnation. Due to high price, and possible carcinogenic effect of hydroxyquinolinolate, USA EPA does not allow registration of this active ingredient.
Nowadays, ethanolamine is a component of several copper based wood preservatives that are available on the market. This includes copper-quaternary ammonium compound, copper dimethyl-dithio-carbamate, and copper azole. In those preservatives, boron, quaternary ammonium compound or azoles are used as cobiocides, and ethanolamine as fixative. However, detailed molar ratios between copper and amine are not known.